The risk of human breast cancer is concerned to cumulative exposure of the breast cells to endogenous estrogens. Strategies aiming at reducing the production of estrogens may be useful for the prevention of estrogens-related breast cancer. Several natural products with plant origin have the potential value as chemo-preventive or therapeutic agents in cancer. Flavonoids, the natural polyphenol compounds, have shown antiviral, anti-inflammatory, anti-mutagenic and anti-carcinogenic activities. Calendula officinalis, a member of compositae family, is well known for its pharmacological effects such as anti-inflammatory, anti-viral, anti-HIV, anti-tumor, anti-mutagenic and cytotoxic properties. Mechanism of the possible chemo-preventing action of flavonoids has not been yet completely understood. They may exert their chemo-preventive and anti-carcinogenic effects in estrogen-dependent cells by inhibiting aromatase, 17?-hydroxysteroid oxidoreductase and other enzymes involved or by possessing estrogenic and anti-estrogenic activities.
In this study, three major flavonoid fractions were separated from a methanol extract of Calendula officinalis flowers by preparative TLC. These fractions were evaluated for inhibition of parent and tamoxifen resistant T47D human breast cancer.
The fractions did not have inhibitory effect. We also examined the effect of quercetin and isorhamnetin on the growth of parent and resistant T47D cells in the presence or absence of tamoxifen. It was found that quercetin increased cell proliferation of the resistant T47D cells at the presence of tamoxifen but no effect was detected by using quercitin itself. In consequence, isorhamnetin had not any proliferative or anti-proliferative activity on the both cell lines. Many mechanisms can contribute to the affects obtained on the cell growth.

The risk of human breast cancer is concerned to cumulative exposure of the
breast cells to endogenous estrogens. Strategies aiming at reducing the
production of estrogens may be useful for the prevention of estrogens-related
breast cancer. Several natural products with plant origin have the potential
value as chemo-preventive or therapeutic agents in cancer. Flavonoids, the
natural polyphenol compounds, have shown antiviral, anti-inflammatory,
anti-mutagenic and anti-carcinogenic activities. Calendula officinalis, a
member of compositae family, is well known for its pharmacological effects such
as anti-inflammatory, anti-viral, anti-HIV, anti-tumor, anti-mutagenic and
cytotoxic properties. Mechanism of the possible chemo-preventing action of
flavonoids has not been yet completely understood. They may exert their
chemo-preventive and anti-carcinogenic effects in estrogen-dependent cells by
inhibiting aromatase, 17ß-hydroxysteroid oxidoreductase and other enzymes
involved or by possessing estrogenic and anti-estrogenic activities.

In
this study, three major flavonoid fractions were separated from a methanol
extract of Calendula officinalis flowers by preparative TLC. These
fractions were evaluated for inhibition of parent and tamoxifen resistant T47D
human breast cancer.

The fractions did not have inhibitory effect. We also examined the effect of
quercetin and isorhamnetin on the growth of parent and resistant T47D cells in
the presence or absence of tamoxifen. It was found that quercetin increased cell
proliferation of the resistant T47D cells at the presence of tamoxifen but no
effect was detected by using quercitin itself. In consequence, isorhamnetin had
not any proliferative or anti-proliferative activity on the both cell lines.
Many mechanisms can contribute to the affects obtained on the cell growth.